The present invention relates to a library unit and a magazine position detecting method in the library unit, and more particularly to a library unit in which an accessor can access any cell of a magazine left in the library unit by detecting the position of the magazine which is pulled out halfway, as well as a magazine position detecting method in the library unit.
There have been proposed various types of methods for positioning a transferring mechanism in a magnetic tape library unit so far.
For example, Japanese Unexamined Patent Publication No. Hei04(1992)-319564 (patent document 1) discloses one of such methods. According to the method, a reflection sensor attached to a medium transferring mechanism (accessor) detects an end or reading mechanism of a cell which loads a medium (tape cartridge). A flag sensor provided for the accessor detects a reference pattern on the flag provided in parallel to a spline for guiding the accessor. The intervals of pulses output from both reflection sensor and flag sensor is measured with use of output pulses of an encoder. The output pulses of the encoder indicate the number of rotations of a motor for driving the accessor. The measuring result is stored in a memory. And during normal positioning, the position at which the motor stops is controlled according to the positional data of the cell read from the memory.
FIG. 11 shows a block diagram of a large capacity external storage unit (magnetic tape library unit) 1100 disclosed in the patent document 1.
The library unit 1100 includes plural cells 1120 for loading plural media 1110; plural reading or writing mechanisms (magnetic tape drives) (not shown) for writing data to or reading data from the plural magnetic tape cartridges; an accessor 1130 for storing each tape cartridge 1110 in or taking out it from each cell 1120 and each magnetic tape drive; a spline 1140 for guiding the accessor 1130; a motor 1150 for driving the accessor 1130; a positioning reference flag 1160 provided in parallel to the spline 1140; a flag sensor 1170 for reading a reference pattern on the flag 1160; and an encoder 1180 for outputting the number of pulses proportionally to the number of rotations of the motor 1150. In another aspect of the invention, the library unit further includes a reflection sensor 1190 attached to the accessor 1130 and used to detect an end surface of each cell 1120; a counter 1101 for counting output pulses of the encoder 1180 while the accessor 1130 is moving; a non-volatile memory 1102 for storing the count of the counter 1101 in relation to the position of each cell 1120; computing means (computer) 1103 for computing a difference between the data in the memory 1102 and a predetermined reference value to control the accessor 1130 by controlling the motor 1150.
In the magnetic tape library unit 1100, the counter 1101 counts the number of pulses outputted from the encoder 1180 between when the end surface of a cell is detected by the reflection sensor 1190 and when the reference pattern is detected by the flag sensor 1170 at the time of periodical inspection. The count value is stored at an address in the memory 1102 corresponding to the position of the cell 1120.
When the accessor 1130 moves and the flag sensor 1170 detects the positioning reference pattern of the flag 1160, the computer 1103 reads the target cell position data from the memory 1102 to compute a difference from the reference value. The difference indicates a relative deviation between the flag 1160 and the target cell 1120 or between the flag 1160 and the target magnetic tape drive. The computer 1103 corrects a predetermined value according to the result of the computing. Then, the computer 1103 controls the motor 1140 so as to stop at a position where the number of pulses outputted from the encoder 1180 matches with the corrected value.
Consequently, because such a relative positional deviation can be corrected in the library unit 1100 disclosed in the patent document 1, the accessor 1130 can be controlled accurately in positioning.